Methods and apparatus for determining properties of a fluid

Abstract

A method and system for determining properties of a fluid involves interacting the fluid with a standing wave in a first state to establish the standing wave in a second state, analyzing an electric signal associated with the standing wave to determine a characteristic associated with the second state, and determining the property of the fluid by comparing the characteristic with a function that associates a plurality of properties with a corresponding plurality of characteristics. The characteristic can include a maximum phase slope, a phase slope associated with a resonant frequency, a maximum magnitude associated with the resonant frequency, the value of the resonant frequency, or any combination thereof.

1. A method for determining a density of a fluid in a biosensing or chemical sensing application, the method comprising:
 interacting the fluid with a standing wave having a first characteristic to establish a second characteristic; 
 measuring a frequency domain signal to determine a resonant frequency of the standing wave; and 
 determining density of the fluid by comparing the resonant frequency with a function that correlates a plurality of densities with a corresponding plurality of resonant frequencies. 
 
   
   
     2. A method for determining a property of a fluid, the method comprising:
 providing an input signal to a resonant device to establish a standing wave in a surface of the resonant device, the standing wave having a first characteristic; 
 interacting the fluid with the standing wave to establish a second characteristic; 
 measuring an output signal of the resonant device in the frequency domain; 
 associating the output signal with the input signal or a reference signal to generate a second signal for selecting a signal value in the frequency domain, the signal value including a maximum phase slope, a phase slope at a resonant frequency, a maximum magnitude, or a magnitude at the resonant frequency of the second signal; and 
 determining the property of the fluid by comparing the signal value to a function that correlates a plurality of fluid properties with a corresponding plurality of signal values. 
 
   
   
     3. A method for determining a viscosity of a fluid in a biosensing or chemical sensing application, the method comprising:
 interacting the fluid with a standing wave having a first characteristic to establish a second characteristic; 
 measuring a frequency domain signal associated with the first or second characteristic to determine a signal value based on a maximum phase slope, a phase slope at a resonant frequency of the signal, a maximum magnitude, or a magnitude at the resonant frequency of the signal; and 
 comparing the signal value to a function associating a plurality of viscosity values with a corresponding plurality of signal values to determine a viscosity value of the fluid. 
 
   
   
     4. The method of  claim 3 , further comprising controlling a temperature of the fluid with a thermoelectric cooler. 
   
   
     5. The method of  claim 3 , wherein the signal comprises a measured output compared to at least one of an input or a reference. 
   
   
     6. The method of  claim 3 , wherein the first characteristic is associated with a first time and the second characteristic is associated with a second time. 
   
   
     7. The method of  claim 3 , wherein the first characteristic is associated with the standing wave in the presence of a first fluid and the second characteristic is associated with the standing wave in the presence of a second fluid. 
   
   
     8. The method of  claim 7 , wherein the viscosity value is associated with the first fluid or the second fluid. 
   
   
     9. The method of  claim 3 , wherein the signal value comprises one or more phase values or phase slope values measured over a bandwidth of frequencies. 
   
   
     10. The method of  claim 9 , wherein the bandwidth of frequencies includes one or more resonant frequencies. 
   
   
     11. The method of  claim 10 , further comprising selecting the signal value from the phase slope at each of one or more resonant frequencies. 
   
   
     12. The method of  claim 3 , wherein the signal value comprises one or more maximum magnitude values measured over a bandwidth of frequencies. 
   
   
     13. The method of  claim 12 , wherein the bandwidth of frequencies includes one or more resonant frequencies. 
   
   
     14. The method of  claim 13 , further comprising selecting the signal value from the maximum magnitude value at each of the one or more resonant frequencies.